Low speed synchronous motor

ABSTRACT

A plurality of stationary poles, each comprising a pair of subpoles, are disposed in opposite relationship with a plurality of rotor magnet poles. The ratio of the number of stationary poles to the number of rotor magnet poles is chosen to be 2:3, 2:5 or 3:5 alternatively. A rotating magnetic field is produced in the array of stationary poles, and for every pi /2 interval of the period thereof, the rotor maintains a stabilized position in which there exists at least one set of a stationary sub-pole and a rotor pole of opposite polarities and attracted to each other. Also in this position, there exist an even number of sets of one sub-pole of a stationary pole and a rotor pole which are of like polarity, are displaced in angular position from each other and repel each other, these different sets producing a balance between their rotating efforts acting upon the rotor.

United States Patent [1 1 Tanaka [11] 3,790,834 Feb. 5, 1974 LOW SPEED SYNCHRONOUS MOTOR [22] Filed: Nov. 11, 1971 [21] App]. No.: 197,872

[30] 1 Foreign Application Priority Data Nov. 21, 1970 Japan, 45/102415 Aug. 4, 1971 Japan 46/58332 [52] US. Cl 310/162, 310/156, 310/257 [51] Int. Cl. H02k 19/02 [58] Field of Search 310/156, 41, 162-164, 310/257 [56] References Cited UNITED STATES PATENTS 3,330,975 7/1967 Osterwalder 310/164 2,432,573 12/1947 .lorgensen n 310/164 3,132,271 5/1969 Midgley 310/162 3,621,312 11/1971 Palmero 310/163 X 2,437,142 3/1948 Welch-et al...... 310/164 3,014,141 12/1961 Riggs 310/164 X 2,951,957 9/1960 Eigeman ..310/164 3,059,131 10/1962 Everardetal. ..310/l64 Primary Examiner-D. E. Du ggan Attorney, Agent, or Firm-Richard C. Sughrue et a1.

[57] ABSTRACT A plurality of stationary poles, each comprising a pair of sub-poles, are disposed in opposite relationship with a plurality of rotor magnet poles. The ratio of the number of stationary poles to the number of rotor magnet poles is chosen to be 2:3, 2:5 or 3:5 alternatively. A rotating magnetic field is produced in the array of stationary poles, and for every 1r/2 interval of v the period thereof, the rotor maintains a stabilized position in which there exists at least one set of astationary sub-pole and a rotor pole of opposite polarities and attracted to each other. Also in this position, there exist an even number of sets of one sub-pole of a stationary pole and a rotor pole which are of like polarity, are displaced in angular position from each other and repel each other, these different sets producing a balance between their rotating efforts acting upon the rotor.

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sum mar 17 BACKGROUND OF THE INVENTION The invention relates to a synchronous motor of small size and low rotating speed suitable for use in watches, clocks, compact timers of various home electrical appliances, measuring instruments and automatic control systems as servo-motor or the like.

Rotary machines incorporating such a synchronous motor customerily employ a reduction gearing for reducing the rotational output therefrom. The use of a reduction gearing increases the cost and causes noises and troubles or failure. A reduction in the rotational speed of the synchronous motor itself would be a solution for this by allowing the reduction gearing to be greatly simplified or even eliminated, thereby reducing the occurrence of failure and noises. The synchronous motor may have its rotational speed reduced by in creasing the number of poles provided. However, such an increase in the number of poles is limited, and particularly for small motors, various technical and economical complications are introduced in so doing.

A motor used in a clock usually comprises a hysteresis motorin view of its attainable accuracy of synchronization with the supply frequency. In a hysteresis motor of the prior art, the amount of rotation of the rotor for one period of the drive current corresponds to twice the pole pitch. A resulting speed of rotation requires the use of a reduction gearing when using such motor as a drive motor of a clock.

Therefore, it is an object of the invention to provide a low speed synchronous motor.

. It. is another object of the invention to providea low speed synchronous motor which is small in size and still can be manufactured readily and inexpensively.

It is a further object of the invention to provide a synchronous motor which provides a low speed of rotation with a reduced number of poles.

It is still another object of the invention to provide a synchronous motor having a speed of. rotation which is one-fifth that of the hysteresis motor of the prior art for the same number of stationary poles used.

SUMMARY OF THE INVENTION In accordance with the invention, a rotor is formed with a plurality of magnet poles which are equiangularly spaced around the shaft thereof, and a stator comprises a plurality of stationary poles equi-angularly spaced around and in opposite relationship with the rotor shaft, each of the stationary poles being constituted by a pair of sub-poles. In the following description, the term rotor magnet pole may be abbreviated as rotor pole simply, it being understood that the term rotor pole always refers to a pole on the rotor that is magnetized in itself or is connected with a magnet on the rotor. Means is provided to produce a rotating magnetic field across the stationary poles. The number of poles on the rotor is different from the number of stationary poles on the stator, and the respective numbers of these poles are chosen such that when one of the sub-poles of a stationary pole assumes an N-pole (or S-pole) by virtue of the rotating field, one of the rotor magnet poles having the opposite polarity of S (or N) comes opposite to that sub pole, by attraction, in correct alignment therewith, there being 'at least one set of statorsub-pole and rotor pole satisfying such'a relationship. In addition, there exist an even number of sets of magnetized sub-poles on the stator which are each associated with a rotor pole located adjacent the magnetized sub-pole and having like polarity as the latter, thus causing a repelling force to act therebetween. The

.repelling forces of two such sets cancel each other,

thereby resulting in a null net rotating effort upon the rotor. Such a rotor position may be referred to herein as a stabilized position.

When the other of the sub-poles of a pair of said stationary pole assumes an N-pole (or S-pole) by rotation of the rotating field, both attracting and repelling forces occur between the stationary poles and the rotor poles to cause a rotation of the rotor in a-given direction, and the rotor again assumes a stabilized position at an angular position where there exist at least one attracting set and an even number of repelling sets of stationary sub-poles on the stator and rotor poles. The similar process is repeated with the rotation of the rotating field to cause a rotation of the rotor until the rotating field ceases to rotate, whereupon the rotor comes to rest at a stabilized position.

With the above arrangement, it is assured that the amount of rotation of the rotor for one period of the rotating field is reduced to less than one pitch of the stationary pole, thereby achieving a rotational speed which is slower than that of the conventional hysteresis motor having the same pitch of stationary poles. When the number of stationary poles remains same, a synchronous motor constructed with a stationary pole number to rotor pole number ratio of 2:3 in accordance with the invention has a rotational speed that is onethird that of conventional hysteresis motor. With a ratio of 2:5 or 3:5, the rotational speed can be reduced to one-fifth that of a conventional hysteresis motor.

BRIEF DESCRIPTION OF THE DRAWINGS Further details of the invention will become apparent from the following description of embodiments thereof taken in connection with the drawings, wherein:

FIG. 1 is a schematic view illustrating a conventional hysteresis motor,

FIG. 2 is a development of the rotor and stator of the hysteresis motor shown in FIG. 1, illustrating its operation,

FIG. 3 is an exploded perspective view of an embodiment of the low speed motor constructed in accordance with the invention,

FIG. 4 is a longitudinal section of the motor shown in FIG. 3, showing its internal construction,

FIG. 5 is a plan view of the-motor of FIG. 4,

FIG. 6 is an exploded perspective view of the motor of FIGS. 3 to 5,

FIG. 7 is a plan view illustrating a rotor having S- poles alone,

FIG. 8 is a development of the stationary poles and rotor poles of the motor shown in FIG. 7 to illustrate its operation,

FIG. 9 is a plan view illustrating a rotor having N- poles alone,

FIG. 10 is a plan view of a motor with separated groups of N- and S-poles,

FIG. 11 is a plan view of another embodiment of the invention having a stator pole number to rotor pole number ratio of 2:5,

FIG. 12 is a development of the stationary poles and rotor poles of the motor shown in FIG. 11, illustrating its operation,

FIG. 13 is a longitudinal section of the motor constructed in accordance with a further embodiment of the invention with a stationary pole number to rotor pole number ratio of 2:10,

FIG. 14 is a bottom view of the motor shown in FIG.

FIG. is an exploded perspective view of the motor shown in FIG. 13,

FIG. 16 is an exploded perspective view of still another embodiment of the invention having a stationary pole number to rotor pole number ratio of 3:5,

FIG. 17 is a longitudinal section of the motor shown in FIG. 16, the rotor portion being omitted from section,

FIG. 18 is a plan view of the motor of FIG. 16,

FIG. 19 is a development of the stationary poles and rotor poles of the motor shown in FIG. 18 for illustrating its operation,

FIG. is a plan view showing another form of the rotor,

FIG. 21 is an exploded perspective view of a motor having its rotor and exciting coil disposed in a common plane,

pitches of the poles 2, or to two pitches of the stationary poles 5.

FIG. 3 shows an embodiment of the motor according to the invention. A cylindrical casing 8 is closed at one end, and receives an internal construction 9 therein,

' the casing 8 being closed by a cover plate 10. Both the FIG. 22 is a longitudinal section of the assembled I motor which is shown in exploded form in FIG. 21,

FIG. 23 is a circuit diagram of an astable multivibration that can be used as a source of excitation, and

FIG. 24 is a longitudinal section of a practical motor constructed, illustrating numerical figures of various parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a conventional hysteresis motor havinga rotor 1 formed with a plurality of magnet poles 2 equi-angularly spaced apart along its periphery, the poles 2 being alternately magnetized as N- and S-poles. In opposite relationship with the outer periphery of the rotor 1, a plurality of stationary poles 5, each comprising a pair of sub-poles 3 and 4 spaced apart in the direction of rotation of the rotor l, are arranged with the same angular interval as the poles 2, thereby constituting a stator 6. A rotating field is produced across the stationary poles 5. The relative positioning of the rotor poles 2 andthe stationary poles 5 is illustrated by a development in FIG. 2. As shown in FIG. 2A, it is assumed that sub-poles 3 3 3 are excited so as to become S-poles while sub-poles 3 3 3 are excited to be N-poles, and that rotor poles 2 2 2 are positioned opposite to the subpoles 3 3 3;, by attraction. As the rotating field varies by an amount of 11/2 from the condition illustrated in FIG. 2A, sub-poles 4 4 4 will be S- poles while sub-poles 4 4 4 will be'N-poles as illustrated in FIG. 2B. Then rotor poles 2 2 2;, will be attracted by sub-poles '4 4 4 respectively, so that the rotor 1 will rotate until the rotor poles come opposite to these respective sub-poles. Further rotation of the rotating field by an amount of 1r/2 will cause the sub-poles 3,, 3 and sub-poles 3 3, to become N-and S-poles', respectively, whereby the into alignment with sub-poles 3 3 3 respectively, as shown in FIG. 2C. Similarly, another 11/2 rotation of the rotating field causes the rotor 1 to assume casing 8 and the cover plate 10 may be injection moulded from synthetic-resin material for the benefits of light weight, low cost and mass production. The internal construction 9 includes a rotary shaft which is rotatably received in bearings l2, l3 integrally formed with the closed end plate of the casing 8 and the cover plate 10, respectively, at the central portions thereof. Bearings 12, 13 are fitted with Teflon members to improve resistance to abrasion and heat, and molybdenum disulfide is coated thereon as lubricant. However, these bearings may comprise more usual construction.

FIGS. 4 to 6 show an example of the internal construction 9. A rotor 14 is secured on the rotary shaft 11, and comprises a disc-shaped permanent magnet 15 which is axially'magnetized, and a pair of pole plates 16 and 17 mounted on the opposite sides of the magnet. As shown in FIGS. 5 and 6, the pole plates l6'and 17 have equi-angularly spaced poles l8 and 19, respectively, which are bent in the opposite directions from the respective plates so as to extend axially at a radius external of the permanent magnet 15. These poles l8 and 19 are angularly displaced from each other by an amount corresponding to one-half the pitch so as to provide an interdigitated structure. The permanent magnet 15 magnetizes the poles 18 and 19 to the opposite polarities, so that N- and S-poles are alternately disposed along the periphery of the rotor 14. While the poles 18 and 19 need not be bent extensions, it is found that the bent, poles as described provide a better efficiency.

In opposing relationship with and around the rotor 14 is an array of alternately disposed stationary poles 20 and 21 with an equal angular interval. Each of the stationary poles 20 and 21 consists of a pair of sub-poles 22,23 or 24, 25 spaced apart in the direction of rotation of the rotor 14. These sub-poles are associated with means for producing a rotating magnetic field thereacross to constitute a stator. In the example shown, a pentagonal magnetic plate 26 has an extension bent at right angles to the same side from each of its apices to fon'n five poles 22, as shown in FIG. 6. In a similar manner, poles 23, 24 and 25 are formed on pentagonal magnetic plates 27, 28 and 29, respectively.

The magnetic plates 26 and 27 are combined together, with a shading disc 30 comprising a copper plate interposed therebetween and with a relative angular displacement, to constitute stationary poles 20. In like manner, the magnetic plates 28 and 29 together constitute stationary poles 21, with a shading disc 31 interposed therebetween. Intermediate the magnetic plates 26 and 28 is interposed a bobbin 32 in concentric relationship with the rotary shaft 11, and an exciting coil 33 is wound thereon. Each of the sub-poles 22 to 25 of 

1. A low speed synchronous motor including a rotor formed with a plurality of magnet poles thereon equi-angularly spaced apart with respect to a rotary shaft, and a stator having a plurality of stationary poles disposed in opposing relationship with the magnet poles on the rotor and equi-angularly spaced apart with respect to the rotary shaft, each of said stationary poles consisting of a pair of sub-poles spaced apart in the direction of rotation of the rotor, said stator being adapted to produce a rotating field across the array of the stationary poles; said motor being characterized in that the pitch of the rotor poles is different from the pitch of the stationary poles, and that in a stabilized position of the rotor, there exists at least one set of angularly coincident and attracting stator sub-poles and rotor poles of opposite polarities and there exist an even number of sets of repelling stator sub-poles and rotor poles of like polarity which are angularly closely displaced from each other, said even number of repelling sets producing respective rotating efforts on the rotor which cancel each other.
 2. A low speed synchronous motor according to claim 1, in which the ratio of the number of stationary poles to the number of rotor poles is chosen to be 2:3.
 3. A low speed synchronous motor according to claim 1, in which the ratio of the number of stationary poles to the number of rotor poles is chosen to be 2:6, and the rotor poles comprises an array of alternating N- and S-poles.
 4. A low speed synchronous motor according to claim 1, in which the ratio of the number of stationary poles to the number of rotor poles is chosen to be 2:5.
 5. A low speed synchronous motor according to claim 1, in which the ratio of the number of stationary poles to the number of rotor poles is chosen to be 2:10, and the rotor poles comprises an array of alternating N- and S-poles.
 6. A low speed synchronous motor according to claim 1, in which the ratio of the number of stationary poles to the number of rotor poles is chosen to be 3:5, and the rotor poles comprises an array of alternating N- and S-poles.
 7. A low speed synchronous motor according to claim 1, in which one-half of the rotor is formed with a plurality of S-poles and the other half of the rotor is formed with a plurality of N-poles, the both N- and S-poles having a common pitch and are displaced from each other by the sum of an integral multiple of the pitch an one-half pitch. 